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Methods: Patients aged ≥18 years and newly diagnosed with NVAF (index date) were identified between 01/01/2006-12/31/2011 within Kaiser Permanente Southern California, categorized by baseline CHADS2 risks, and followed until 12/31/2012. Longitudinal analyses examined time-varying antithrombotic treatment episodes for each individual patient. The unadjusted and adjusted relative risk (RR) of stroke/SE was reported from generalized estimating equation models for 6 different treatment episodes: 1) warfarin time in therapeutic range (TTR) ≥55%, 2) warfarin TTR <55%, 3) off warfarin, 4) on aspirin (ASA), 5) off ASA, and 6) never on antithrombotic therapy.

Results: Among 23,297patients with CHADS2 ≥1, 1,782 stroke/SE events occurred during 60,021 person-years of follow-up. The warfarin TTR ≥55% category had the lowest stroke/SE rate (Rate = 0.87 per 100 person-years, 3.23 TTR<55%, 4.38 off warfarin, 3.11 ASA, 3.81 off ASA, and 3.76 never on therapy). Warfarin TTR ≥55% was associated with a 77% lower risk of stroke/SE, and ASA was associated with a 27% lower risk of stroke/SE compared to never on therapy (adjusted RR [95% CI] = 0.23 [0.19-0.29], 0.73 [0.65-0.82] respectively). Warfarin TTR <55% was only marginally associated with the stroke/SE reduction compared to never on therapy (adjusted RR = 0.83 [0.70-0.99]). The stroke/SE risk for off warfarin and off ASA were not statistically different from never on therapy. Other significant factors associated with stroke/SE included older age, female, Black or Hispanic race, having diabetes, hypertension, previous stroke/TIA, peripheral vascular events, higher comorbidity score, and not having a major bleed.

Conclusion: Warfarin TTR ≥55% was associated with the greatest reduction in stroke/SE among the antithrombotic treatment groups examine here. Future studies should examine modifiable factors to improve outcomes for patients with warfarin TTR <55% or those who are off antithrombotic therapy.